This time in our grasping genetics series, we’re going to use a stallion who has a complex genetic makeup, a makeup that can be quite confusing – introducing Lena's Frosted Jag.

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Our Baseline

In order to understand what’s happening with this particular stallion, we must also know that most animals (dogs, cats, horses, etc.) start at the cellular level as a solid black coat base. On top of this black coat base is then stacked a series of possible genetic modifications, patterns, and diseases. This “stack” of genetic modifications brings us our end result, and in some cases, our physical expression. However, that’s not a hard fast rule as many horses carry minimally expressed markers (heterozygous but not expressed, or minimally expressed – in the case of Tobiano, Overo or Dominant White patterns for example; or covered up by a dominant gene such as gray).

We chose a really beautiful but genetically complex stallion for this deep-dive because of the physical expression of his genetics. For the sake of simplicity, for any set of gene markers that is not present on either allele (those marked N/N) we are going to skip (such as silver, champagne, etc.). Only those with at least one allele present (heterozygous) will be shown below:

Here’s a bit of a photographic journey that shows Jag from foal age, where he’s very clearly visually dunskin, to where he is as a 5-year-old, looking beautifully silver. You’ll also note that some of his primitive markings are beginning to wash out very lightly, which may increase over time to the point where they too are “hidden” gems within his genetic story.

To truly understand what’s taking place here, let’s first define what each of these markers means and how it will behave when stacked upon other genes, and which genes are “dominant” and will win out in the game of physical expression.

Red Factor: In this case we know that our sample stallion is homozygous (black), this determines his ability to pass the gene on and his physical expression. We know that he will never pass red factor to his foals. This genetic marker is a bit confusing because it is essentially a gradation of how much or how little red factor will be expressed; a heterozygous horse (E/e) will produce 50% black pigmented foals and 50% red foals, and those with the (e/e) genotype will never express black (always be red). Note, as we discussed in our homozygous vs. heterozygous article, a homozygous black horse does not mean that the horse’s coat will be solid black, but that the horse will be either bay (depending on their agouti status) or solid black.

Agouti: This gene controls where the black pigment is expressed. With our example, he is homozygous (A/A) which means that his black will be pushed to the points (legs, ears, tail, mane, forelock, nose, etc.). He will pass at least one allele to 100% of his foals, which means all of his foals will be bay and never solid black. Only horses with “a” for both alleles resulting in (a/a) will be true black horses (which is much more rare). In the genetic lottery, the horse’s genetic makeup must be (E/E, a/a) to be solid black, and since we know that Jag is homozygous agouti (A/A), he will always pass on at least one ‘A’ allele and never allow for an (a/a) pair of alleles in his offspring.

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Our north star: The three core base colours

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Cream: This gene controls the dilution of the coat base (and from what we know about the above (Red Factor & Agouti), his base is bay for the moment). We will dive more into what these dilutions are and how they interact with the different coat bases (black, bay, and chestnut/sorrel). But for the use of this article, we know that our stallion carries a single copy of the cream dilution (n/Cr); he will produce diluted foals 50% of the time, as he himself is a dilution on top of bay, whereas his sire is a double dilution of bay (Perlino) and would always produce single dilution foals. The single dilution for the bay gene is buckskin.

So, we know right now that we have a gorgeous buckskin base for which to stack more genes atop. As we unpack more of his genetic markers you will see how things transform from this point forward.

Dun: This gene is a bit more complex because there are five variations. For Jag, this particular combination means that he will express dun dilution by way of his “D” allele, and that he will also express primitive markings due to the “nd2” allele. He can pass both of these markers on 50% of the time. We will dive into the dun markers in more detail with photographic examples in a later article. But for now, let’s understand that Jag will have both primitive markings as well as the dun dilution of the body.

At this juncture, we now know that our stallion is a buckskin dun (commonly called dunskin).

But here’s the twist...

Gray: Jag here has gray present – gray itself is a dominant gene, which means that if the horse carries gray at all, it will be expressed (and as we know, this may take time, the foal may grey out quite young, or later as they mature).

With all of his coat markers stacked one on top of the other, we know that Jag is a stallion who started his life as a dunskin from a strictly visual perspective. But with the power of genetic testing, and because he has changed over the course of his life – he now continues his life appearing as a ‘gray’ dun. He “hides” his underlying buckskin base due to the dominant gray gene essentially “wiping” the base slate clean (visually). Regardless of this gray presence, his “hidden” genetics will still be passed down in the lottery of genes he and any paired mare will offer any foals.

What will he produce when you breed to him? That’s an interesting question, and one that’s hard to really answer succinctly simply because your mare’s genetics play a large role here as well. But if we were to take a basic combination of a chestnut mare we can figure out the percentages of different coat results.

Here are some sample genetics for our made-up red mare, we’ll call her Ruby:

Ruby is a solid red, she carries no hidden genetics, but when paired with a powerhouse of gene possibilities like Jag – their combined genetics have the following possible outcomes:

Note that 55.6% (5) of the 9 resulting gene combinations would be gray in expression visually (eventually). However, under that gray would be a complex gene set that would be passed on to subsequent foals.

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Imparting genes: Jag's parents and how he ended up being as unique as he is

As a bit of an aside, we also have a full brother to Jag to compare genetics from, simply to illustrate the variety of genetics certain pairings can provide. Their sire 'Bar Lenas Last' is a perlino dun (a bay dun + 2 Cr alleles = perlino dun), while their dam, 'Letas Blue Best' is a Gray Bay (born bay with dominant n/G gene, making her gray over time).

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His full brother, Lenas Blue Hickory's genetics are as follows:

Compared to Jag, this colt differs greatly in that he didn’t inherit double alleles for any gene marker, making him heterozygous for everything on his panel. He’s also a dunskin, but has a different variation of dun zygosity (nd1/nd2). He also inherited the gray (n/G) and is slowly graying out over time.

As fascinating as genetics are, they are just the fancy wrapping our horses are in, there’s something to be said for beauty and eye-appeal, but beyond that – Jag is a gorgeous, well-built athlete who’s siring wonderful foals.

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Have questions?
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